What is a Surge Protector?

A surge protector – also known as a surge suppressor, spike suppressor, transient voltage surge suppressor (TVSS), or surge diverter – is the name given to a broad group of devices that are designed to react to sudden or momentary overvoltage conditions.

Surge protectors serve as protective devices, preventing equipment damage caused by abnormal conditions.


Surge Arrester vs Surge Protector

A surge arrester (or lightning arrester) serves the same purpose as a surge protector: they protect electrical equipment from over-voltage conditions. They are both commonly referred to as SPDs (Surge Protection Devices).

The difference between the two is the scale of the protection. Surge arresters are for large-scale protection (medium to high voltage), while surge protectors are for small-scale protection (low voltage). Surge protectors can be appliance-specific – such as a surge protector for washing machine or a surge protector for refrigerator – or a whole house surge protector.

Surge arresters (or lightning arresters) are used by utility companies in power transmission and distribution systems to protect their electronic equipment and infrastructure. They can also be found in large-scale industrial operations, such as mining or oil and gas.

These protect against extremely large fault currents, such as those caused by lightning – hence the name “lightning arrester”. They look like this:

Surge protectors are used to protect domestic and consumer electrical equipment. They protect electronic appliances in your home like your computer, television, and refrigerator.

Clamping Voltage

The clamping voltage refers to the maximum amount of voltage that can pass through a surge protector (or electrical breaker) before it restricts further current from passing through it.

Because of this, surge suppressors are sometimes called “Transient Clamps”.

Clamping the voltage’ refers to constricting the voltage when a transient voltage spike is detected above the clamping voltage. You can use a good multimeter to measure the voltage across an electrical breaker.

Surge Protector Standards

There are many national and international standard related to surge protectors. Some of the most prominent include:

  • IEC 61643-11 Low-voltage surge protective devices – Part 11: Surge protective devices connected to low-voltage power systems – Requirements and test methods
  • IEC 61643-21 Low voltage surge protective devices – Part 21: Surge protective devices connected to telecommunications and signaling networks – Performance requirements and testing methods
  • IEC 61643-22 Low-voltage surge protective devices – Part 22: Surge protective devices connected to telecommunications and signaling networks – Selection and application principles
  • EN 61643-11, 61643-21, and 61643-22
  • Telcordia Technologies Technical Reference TR-NWT-001011
  • ANSI/IEEE C62.xx
  • AS/NZS 1768 Lightning protection (Standards Australia)

Types of Surge Protectors

The types of transient voltage suppressors:

  • Decoupling Capacitors
  • Zener Diodes
  • Transient Voltage Suppressor Diodes (TVS Diodes)
  • Metal Oxide Varistors (MOVs)
  • Avalanche Diode
  • PolySwitch

Decoupling Capacitors

Decoupling capacitors (also known as bypass capacitors) are used to decouple (i.e. separate) two parts of an electrical circuit. 

Where they are used

  • Low power applications
  • Simple circuits


  • Very low cost
  • Simple to maintain
  • Fast acting


  • Requires multiple capacitors of different sizes for complete protection
  • Uneven suppression

Zener Diodes

Normal diodes only let current flow in one direction – from its anode to its cathode. A Zener diode is a special type of diode that allows current to flow (functionally and predictively) in the reverse direction – from its cathode to its anode – once the voltage through the diode reaches a certain level.

This required level of voltage to allow current to flow in the reverse direction is known as the Zener voltage.

This Zener voltage will be maintained even when a large amount of current flows through the Zener diode. This attribute of a Zener diode is harnessed when using a Zener diode as a transient voltage suppressor.

The Zener Diode is purposefully used in its “reverse bias” or reverse breakdown mode, with the Zener voltage equal to the desired output voltage. The load is kept in parallel with the Zener diode, allowing the Zener diode to act as a shunt regulator. The Zener diode conducts the excess current and hence maintains a constant voltage across the load.

Note that although the voltage is being suppressed, the Zener diode is acting more like a voltage regulator rather than a voltage suppressor. It is not optimal for use cases where voltage must be abruptly clamped.

Where they are used

  • High-speed data lines
  • High-frequency circuits
  • Clamping in low-energy circuits


  • Low cost
  • Simple to maintain
  • Fast acting
  • Bidirectional 
  • Usually fail open (as opposed to fail short)


  • Only usable in low-voltage systems (note this is because Zener voltage = output voltage, and Zener voltages are not very high)
  • Need to be careful to ensure minimum Zener Diode current is maintained

Transient Voltage Suppressor Diodes (TVS Diodes)

Where they are used

TVSs are commonly used in data transmission systems. This is due to their:

  • Quick response time to overvoltage conditions
  • Longevity
  • Low clamping voltage

All three of these benefits are desirable features in a data transmission system, which are usually (1) extremely sensitive to damage caused via overvoltage (2) in areas which are not easily accessible or frequently visited and (3) typically operate at a low voltage.


  • Low cost
  • Simple to maintain
  • Fast acting
  • Bidirectional 


  • Only usable in low-voltage systems

About Blake Sutton

Blake has worked as an electrician for over 10 years, receiving his Journeyman Electrician license in 1998. Looking to take his professional electrical career further, in 2008 he received his Bachelor of Science in Electrical Engineering (BSEE) from the University of Texas in Austin. Blake now works full time as an electrical engineer, specializing in power systems.